Charczenko, N.

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PARACHIT_ I_B_OB]L_E AT SLV_RSOHIC SPB_DS
By Nickolai Charczenko
The recovery o_ high speed vehicleF created a new rematremeat in
recovery operations, decelerators have to perfo,_, at ver_ high altitudes
aud supersonic speeds. Al.th_ugh the require_ents have =barBed, t,he basic
considerations in the selections of drag devices.- essentially remain the
same for the supersonic speed range as they were forstJ_onic. The fol-
lo_ug slide show these basic reQu4_rements, they are:
Slide Z
Based on these requlrements, conventional perachu=e_ _ppe_r to be
well suited for this Job, _n vle,a of the fact that they have keen _roven to
be hlghly tellable in subsonic operations. _hey have an apparent weight
advantage over other non_-i£tlng type_ of decelerator_ and _e were more
famLlier with parachutes than any other drag devices. For these reasons,
they were n natural choice for supersonic speed range. Rowev_r, tests at
supersonic speeds reve_led some prob)em areas of parachute perfor_ance.
The thzee major prGblem areas are:
Slide IZ
We vere prlma-_l:, concerned with e.he first c_o of these problem crees
at supersonic speeds, whlch we _r111 consider at this time. _..:-: th._rd one
can be antici?ated in the future.
Slide III
The e_perimental results of flexible r_on-_oe parach,_tes ind,.cats
two major areas o_ parachute instability: osc.'11atory motion of the para-
chute sbo_t the point o_ attachment and shock pattern fluctuations accom-
panied b'! a violent _'anopy ._._'ca_-hing along with reduced infIa_ton and
drag c_rscteristics. The latter _hich is referred to as in_lation
https://ntrs.nasa.gov/search.jsp?R=19730061713 2020-03-17T13:38:28+00:00Z
instability has been the sub_ect of co,-si_erable investigation. The basic
problems involved in the inflat_eninstab_iity are high rates at _.ich the
shock is alternately swallowed _nd ext.ell_d (somewhat analogous to the _n-
let buzz phehomenon) and the interaction beL_e_n the boe_ary layer on t_.e
individual shroud lines and _le shock wave in frcu_ of the parachute canopy.
Tb.is type of instability causes large variatiou_ in drag _th fre0_encies
exceeding 100 cps.
Slide IV
The next sli_e shows some parachutes e_ployed in s_personLc speeds.
The bottom one is a tyvlc_l ribbon parachute used in _os_ _f _he investi-
gations. Various means have been tried with this type of parachute _o
elin_'.nate inflation instability such as varying porosity, var_J._g number
cf shroud lines, e_tending the skirt, _acb_ng az, inflated tube to the
skirt and others, but only limited success was at. laved by these _a_ns.
It was evident bynow that the best we can hope for, in light of the fact
that the fluctuations in shock pattern exist even for the rigid p_achute
models in the free stream as far as shock fluctutation_ ace concerned, i6
to reduce their influence on the breathing of c ps:_chute. I believe thl6
has been achieved to a !_ degree wi_h _he parachute designed by Cook
Research Laboratory, under an Air Force conCrsc_. These parachutes are
radically dlffer_nt from most parachu_ deslgn_. Thelrmain featuresbeing
low porosity conical inlet canopies and high porosity flat roofs. Both
of these designs have performed satisfactorily Ir the Math number ra_e _f
2.30 tO 4.65. A high sp_ed schileren mo,-ies showin_ stability of these
parachutes will be shown later.
Slide V
- 2-
4
"3
.!
i
As far pA ct_ drag of ._ech_:'_e_ is c_ncerued, we vouZ_ like to h_ve
• drag coefficient of 0.5 _r bztt_:: for parachuter st supersonic _.edw,
The ne_.c ,elide shove a drec level :Eor v_rJoue drag de-ices. Here the
dra_ coefficient is plot-ed versus Math number at ten base dl_ueters
":ownstresm i ,r par.echutes and rls_,_ tppes of drcg devices. D,-.a 8 coef-
ficient fo'_" nee _. ribbon type _,a:-achu_es fells £_ thi_ resio._ . The conical
'_slat canopy has i_pxoved the drag c_efficien_ of pare'.hutes as shown in
this slide. Even though co_,eid,.ral_e lxuprovement __r. g re S coefficient
a.._ stab_!ity wa_ achieved with the conical inlet parachutes, the varia-
tions in dr_ _till existed, thoush to • lecser degree than _rlth ribbon
type parachu:e_. Due t,, the problem areas encounte_-ed with psr achx:te_
operations _c supersonic speeds, other _.ra E devices were being developed
conc,:=rently er.d a -om_arieon in dr_g coefficient between them anO _a£s-
chutes _s mad,: in this slide. Ic can be snen tbet the dra_ _efficient
of parachutes c_ '.;e ex.eeded by a re=cox of c_o to _hree ['y -:.._ _'t_d
type c'e=ele---or_ Thus there is s wide m_rs!n _-_ d_a_ coeff_e,'_t "._st
can be used u_ a tredeoff for ve£shc. Rig£d ant ir_f_;_able t_,,e. of _ece].-
erators will be d-_'scussed in morz uetail in the _ollo_",q_ p_per.
In this invesclge_.icn, no _rt _ae made to establish resists of
optium_. _.erformance; however, from visual obeerve_ions of chess s_d other
tests a-'d from :-igh' speed schlieren mo.,£es, it was ev_-,_ut that. t_e perform-
en_.e of the p_rschut,ee v_s _;'=-_depe.ndenc. A _eke study for varlous bodies
to about 15 base dleu_:=_.rs downstr_a_ of the _'ehlcle _ould 1,e u_st helpful
_u anslyzi_s and pc_-t_lv explaiuinS the vsr_et!o_ insts_l£ty and, st
sou_. L_,:h numbers, de,--.aase in dra R coefficient _ich 4_screens 1_ tra_.liu_,
_lstsnce. I think our biggest _.roblem in the develop_r,; _f stable
-3-
Ip_:_-xebutss ior c;,e s_rsoa!e spe,_J rans,_ has bees _e lack o£ sde.=uete
theo: 7 I_ geL_de the investigation. C_equ.-ntly, most o£ the _._k has
_r
°
r
-°
bee_ done on e .t_al end error _tsis. -
_e uine_ .tmmels are ue[t suLtt_l f_- the r-search of deceleretors
L_:mme the par_tr/c study emder a v_de wt_eLy-o_ test c_dltLoul #_u_
Wr _ts_ty S/smis-_e_. Rovever, _[te-r • _o_:.ab!e der_u has been evolved
i_ the u_nd-tumusl -testiu_,.thls-should be au_-._te4 oy £tee fltKht test_
tc che_.k out the syste_. :_nder _ ec_ :_t co_d_t!ons. Free. f_._f.:
tests are b_J_ ¢_._asider_ to c_eck o_. psx-ach_e8 "_hst h_J _ttlsfac_o_-_-.
_ NO_C_T_r_ C_AL _A_
._-_me :_plorato_ _or_ has _ m perf_r_-_i on the ror.¢ms_m_l_-m! t}_m
perachu_e_ i_. the vlml _mei _t SUl_:rso_de sp_ed_. _ase are ps_-achu_es
_th _hlgh rotational ;peeds,.'-y_ica_ r._.pre:;e_: ;atzo_ -_£ _h/ch ere vertex
rt_ para___:.-t_ m_i rot&£oil. Both o_ the ab._e _mtlcae_; _0de18 tere
t_.st-..'_ at supersoulc speeds, b, t they ":=tied be.'.o::e aa_ _i&--.._tflC.a_t dry&
r:.a_-_r_eu_s c_ul_ be ob_i.oed. '_eve_- a xlsual, ch_-.k, of dta_ indlca_or
_8
°
before £eilu_e _ =urr.-d sho_ed hJ_h draK %_.ue_ itt some cases. Further
resort _ aloes _hese .llne_ _uld be warrante_.
hi._h sp_d movle_ thac ver¢. c_t'_l_.d in , :'e_r seconds of their op_rs-
_r_ton will be prese._ced a_ ch_ rt-_ aloe $ _rlrl_sc_,!leren movies of the
previously _iscus_._i pcrachut_ models.
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Parachute performance at supersonic speeds

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